1. Field of the Invention
The present invention relates to a noise reduction device and a noise reduction method that reduce a noise in image data by using a blackout image that is taken while an image sensor is shaded.
The present invention also relates to an electronic camera incorporating the noise reduction device.
The present invention also relates to a program that makes a computer operate as the noise reduction device.
2. Description of the Related Art
In general, a fixed pattern noise appears in image data when the image data is taken by an electronic camera during long exposure.
Japanese Unexamined Patent Application Publication No. 2000-125204 (see claims 1 and 2, for example) discloses a device for removing the above fixed pattern noise. In this conventional device, image data taken in a normal manner and blackout image data taken while a shutter of the electronic camera is closed are prepared first. This conventional device subtracts the blackout image data from the normally taken image data, thereby removing the fixed pattern noise in a common mode.
However, the blackout image data taken during long exposure includes a random noise, in addition to the fixed pattern noise. The random noise is added in a reversed mode to the normally taken image data in the aforementioned subtraction by the conventional device. Thus, there is a problem in that the random noise in the image data is increased.
Moreover, it is necessary to make charging time of the normally taken image data and charging time of the blackout image data equal to each other in the conventional device in order to make the fixed pattern noises in both the normally taken image data and the blackout image data equal to each other. Thus, in a case of a 10-minute exposure, for example, it takes further 10 minutes to obtain the blackout image data. During that period, shooting by the electronic camera cannot be performed. Thus, a valuable opportunity for a photograph may be missed.
Furthermore, memory consumption is increased in the conventional device because the blackout image data is temporarily stored in a memory.